1. Field of the Invention
This invention relates to a dielectric fluid composition and, more particularly, it pertains to mixtures of atomized dielectric fluids and insulating gases for high electrical strength.
2. Description of the Prior Art
As a general rule, the higher the density of an insulating liquid or gas, the higher is its electrical strength. Sulphur hexafluoride (SF.sub.6) gas, for example, is about five times denser than air and has a breakdown strength which is about 2.5 times higher, while compressed SF.sub.6 has even higher dielectric strength. One problem in compressing a gas to obtain a high electrical strength is that a stronger vessel is needed to contain the gas. Another consideration is the high cost of SF.sub.6 when large quantities are required, as in the case with transmission lines. As pointed out in U.S. Pat. No. 4,162,227, it is for these reasons that gas mixtures are employed, so that a high strength, high cost, dielectric gas may be mixed with a poorer one of lower cost, to provide a mixture with a dielectric strength somewhere between the strength values for each of the two mixture components. Also, in the same patent it is noted that for some gas mixtures, the dielectric strength may be higher than either component strength at the same temperature and pressure of the mixture.
In U.S. Pat. No. 2,990,443 a gas-insulated transformer is described in which SF.sub.6 gas provides the insulation. To remove heat during the transformer operation, an atomized fluid is introduced into the SF.sub.6 gas and circulated throughout the transformer windings and core. It is inferred that the atomized fluid does not reduce the dielectric strength of the SF.sub.6, and it is emphasized that the function of the SF.sub.6 is to provide electrical insulation.
As can be seen from the discussion of the prior art, it is well known that certain gas mixtures can have a high electrical strength, and that an atomized fluid can be mixed with SF.sub.6 without reducing the electrical strength of SF.sub.6. It is an object of this invention to provide a gas/atomized fluid mixture of much higher dielectric strength than the gas at the same temperature and pressure. Another object of this invention is to define the range of droplet sizes required in order to the gas/atomized fluid to have a high dielectric strength. A further object of this invention is to provide a method of atomizing a dielectric fluid and introducing the droplets into the gas. Other features and merits of this invention will appear hereinafter.